A head to head comparison of the Montana 2020 Primary gives us an idea of the break down of the voters.
Donald Trump received 200,174 (60%) votes to beat Joe Biden, who received 111,706 (34%) votes and Bernie Sanders, who received 22,033 (7%) votes.
In the Primary, Trump won 52 counties in the 3-way match up. Biden trailed behind Trump winning 4 counties with Sanders winning nothing in Montana Primary.
Bernie Sanders vs Joe Biden
Joe Biden vs Donald Trump
Donald Trump vs Joe Biden
In the head to head match ups, Biden (84%) beat Sanders (16%). Trump (90%) beat Sanders (10%). Also, Trump (64%) beat Biden (36%).
These 10 counties play an important role in these primary elections. Even if a candidate can get a sizable majority in the larger counties (Yellowstone and Missoula), it is possible for the other candidate to catch up from the smaller counties.
Trump won Yellowstone county, giving him a 14k vote advantage over Biden and a 27k advantage over Sanders. He also won 51 other counties in Montana, leading to him beating his opponents in these Primary elections.
Related References: 2016 Montana General Election Story, 2016 Montana Primary Election Story